PENELOPE 2003 - OECD Nuclear Energy Agency

6.2. Examples of MAIN programs 191
source. The programs can be easily generalized to the case of multi-particle sources with
continuous (or discrete) energy spectra. For details on the operation of these codes, see
section 6.2.4 below and the heading comments in the corresponding source files.
6.2.1 Program PENSLAB
The program PENSLAB simulates electron/photon showers within a material slab (see
fig. 6.2). It illustrates the use of the simulation routines for the simplest geometry (as
geometry operations are very simple, this program is faster than the ones described
below). The slab is limited by the planes z = 0 and z = t, the thickness. The lateral
extension of the slab is assumed to be infinite, i.e. much larger than the maximum range
of the particles). Primary particles start with a given energy E 0 from a point source
at a given “height” z 0 (positive or negative) on the z-axis, and moving in directions
distributed uniformly in a spherical “sector” defined by its limiting polar angles, say θ 1
and θ 2 , which is indicated by the hatched wedge in fig. 6.2. That is, to generate the
initial direction, the polar cosine W = cos θ is sampled uniformly in the interval from
cos θ 1 to cos θ 2 and the azimuthal angle φ is sampled uniformly in (0,2π). Thus, the case
θ 1 = 0 and θ 2 = 180 deg corresponds to an isotropic source, whereas θ 1 = θ 2 = 0 defines
a beam parallel to the z-axis. Notice that the complete arrangement has rotational
invariance about the z-axis.
➤
z
➤
E
θ
➤
t
➤
x
θ
➤
E 0
y
➤
z 0
source
Figure 6.2: General planar geometry considered in PENSLAB.
PENSLAB generates detailed information on many quantities and distributions of physical
interest. The output files contain a self-explanatory report of the simulation results,
which consist of:
(i) Fractions of primary particles that are transmitted, backscattered and absorbed
and a number of average quantities (track length within the sample; number of
events of each kind per particle; energy, direction and lateral displacement of
particles that leave the sample, etc.).
(ii) Energy distributions of transmitted and backscattered primary particles.